Question

我正在用dotet核心3.1，ef核心3.14和postgres 12构建Blazor应用程序。最初，我一直在使用Visual Studio附带的mssql localdb来构建应用程序，但一切进展顺利，但是后来我改变了到postgres，运行良好的迁移并创建了所有表，但是当我向表中添加数据时，出现“重复键值违反唯一约束”错误。我认为这是因为在dotnet核心中创建一个新对象时，它会将Id字段初始化为0，而postgres似乎不明白，需要将其更改为表中的下一个可用数字。到目前为止，我已经尝试按照https://www.npgsql.org/efcore/modeling/generated-properties.html这里的文档将以下内容添加到我的dbcontext OnModelCreating中。

modelBuilder.Entity<Grade>()
        .Property(p => p.Id)
        .UseIdentityAlwaysColumn();

以及以下内容分别尝试

 modelBuilder.Entity<Grade>()
        .Property(p => p.Id)
        .ValueGeneratedOnAdd();

这些都不是解决问题的方法，所以我还尝试将以下修饰添加到模型的Id字段中。

[DatabaseGenerated(DatabaseGeneratedOption.Identity)]

如果有帮助，这是完整的错误消息

    fail: Microsoft.EntityFrameworkCore.Database.Command[20102]
      Failed executing DbCommand (14ms) [Parameters=[@p0='?' (DbType = Double), @p1='?'], CommandType='Text', CommandTimeout='30']
      INSERT INTO "Grades" ("MinimumSalary", "Name")
      VALUES (@p0, @p1)
      RETURNING "Id";
fail: Microsoft.EntityFrameworkCore.Update[10000]
      An exception occurred in the database while saving changes for context type 'EmployeeManagement.Api.Controllers.PayrollContext'.
      Microsoft.EntityFrameworkCore.DbUpdateException: An error occurred while updating the entries. See the inner exception for details.
       ---> Npgsql.PostgresException (0x80004005): 23505: duplicate key value violates unique constraint "PK_Grades"
         at Npgsql.NpgsqlConnector.<>c__DisplayClass160_0.<<DoReadMessage>g__ReadMessageLong|0>d.MoveNext()
      --- End of stack trace from previous location where exception was thrown ---
         at Npgsql.NpgsqlConnector.<>c__DisplayClass160_0.<<DoReadMessage>g__ReadMessageLong|0>d.MoveNext()
      --- End of stack trace from previous location where exception was thrown ---
         at Npgsql.NpgsqlDataReader.NextResult(Boolean async, Boolean isConsuming)
         at Npgsql.NpgsqlCommand.ExecuteReaderAsync(CommandBehavior behavior, Boolean async, CancellationToken cancellationToken)
         at Npgsql.NpgsqlCommand.ExecuteDbDataReaderAsync(CommandBehavior behavior, CancellationToken cancellationToken)
         at Microsoft.EntityFrameworkCore.Storage.RelationalCommand.ExecuteReaderAsync(RelationalCommandParameterObject parameterObject, CancellationToken cancellationToken)
         at Microsoft.EntityFrameworkCore.Storage.RelationalCommand.ExecuteReaderAsync(RelationalCommandParameterObject parameterObject, CancellationToken cancellationToken)
         at Microsoft.EntityFrameworkCore.Storage.RelationalCommand.ExecuteReaderAsync(RelationalCommandParameterObject parameterObject, CancellationToken cancellationToken)
         at Microsoft.EntityFrameworkCore.Update.ReaderModificationCommandBatch.ExecuteAsync(IRelationalConnection connection, CancellationToken cancellationToken)
        Exception data:
          Severity: ERROR
          SqlState: 23505
          MessageText: duplicate key value violates unique constraint "PK_Grades"
          Detail: Key ("Id")=(1) already exists.
          SchemaName: public
          TableName: Grades
          ConstraintName: PK_Grades
          File: d:\pginstaller_12.auto\postgres.windows-x64\src\backend\access\nbtree\nbtinsert.c
          Line: 570
          Routine: _bt_check_unique
         --- End of inner exception stack trace ---
         at Microsoft.EntityFrameworkCore.Update.ReaderModificationCommandBatch.ExecuteAsync(IRelationalConnection connection, CancellationToken cancellationToken)
         at Microsoft.EntityFrameworkCore.Update.Internal.BatchExecutor.ExecuteAsync(IEnumerable`1 commandBatches, IRelationalConnection connection, CancellationToken cancellationToken)
         at Microsoft.EntityFrameworkCore.Update.Internal.BatchExecutor.ExecuteAsync(IEnumerable`1 commandBatches, IRelationalConnection connection, CancellationToken cancellationToken)
         at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.SaveChangesAsync(IList`1 entriesToSave, CancellationToken cancellationToken)
         at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.SaveChangesAsync(DbContext _, Boolean acceptAllChangesOnSuccess, CancellationToken cancellationToken)
         at Npgsql.EntityFrameworkCore.PostgreSQL.Storage.Internal.NpgsqlExecutionStrategy.ExecuteAsync[TState,TResult](TState state, Func`4 operation, Func`4 verifySucceeded, CancellationToken cancellationToken)
         at Microsoft.EntityFrameworkCore.DbContext.SaveChangesAsync(Boolean acceptAllChangesOnSuccess, CancellationToken cancellationToken)
Microsoft.EntityFrameworkCore.DbUpdateException: An error occurred while updating the entries. See the inner exception for details.
 ---> Npgsql.PostgresException (0x80004005): 23505: duplicate key value violates unique constraint "PK_Grades"
   at Npgsql.NpgsqlConnector.<>c__DisplayClass160_0.<<DoReadMessage>g__ReadMessageLong|0>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at Npgsql.NpgsqlConnector.<>c__DisplayClass160_0.<<DoReadMessage>g__ReadMessageLong|0>d.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at Npgsql.NpgsqlDataReader.NextResult(Boolean async, Boolean isConsuming)
   at Npgsql.NpgsqlCommand.ExecuteReaderAsync(CommandBehavior behavior, Boolean async, CancellationToken cancellationToken)
   at Npgsql.NpgsqlCommand.ExecuteDbDataReaderAsync(CommandBehavior behavior, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.Storage.RelationalCommand.ExecuteReaderAsync(RelationalCommandParameterObject parameterObject, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.Storage.RelationalCommand.ExecuteReaderAsync(RelationalCommandParameterObject parameterObject, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.Storage.RelationalCommand.ExecuteReaderAsync(RelationalCommandParameterObject parameterObject, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.Update.ReaderModificationCommandBatch.ExecuteAsync(IRelationalConnection connection, CancellationToken cancellationToken)
  Exception data:
    Severity: ERROR
    SqlState: 23505
    MessageText: duplicate key value violates unique constraint "PK_Grades"
    Detail: Key ("Id")=(1) already exists.
    SchemaName: public
    TableName: Grades
    ConstraintName: PK_Grades
    File: d:\pginstaller_12.auto\postgres.windows-x64\src\backend\access\nbtree\nbtinsert.c
    Line: 570
    Routine: _bt_check_unique
   --- End of inner exception stack trace ---
   at Microsoft.EntityFrameworkCore.Update.ReaderModificationCommandBatch.ExecuteAsync(IRelationalConnection connection, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.Update.Internal.BatchExecutor.ExecuteAsync(IEnumerable`1 commandBatches, IRelationalConnection connection, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.Update.Internal.BatchExecutor.ExecuteAsync(IEnumerable`1 commandBatches, IRelationalConnection connection, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.SaveChangesAsync(IList`1 entriesToSave, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.SaveChangesAsync(DbContext _, Boolean acceptAllChangesOnSuccess, CancellationToken cancellationToken)
   at Npgsql.EntityFrameworkCore.PostgreSQL.Storage.Internal.NpgsqlExecutionStrategy.ExecuteAsync[TState,TResult](TState state, Func`4 operation, Func`4 verifySucceeded, CancellationToken cancellationToken)
   at Microsoft.EntityFrameworkCore.DbContext.SaveChangesAsync(Boolean acceptAllChangesOnSuccess, CancellationToken cancellationToken)```

Answer 1

对于其他遇到相同问题的人，Postgres有一个限制：如果您为数据库添加种子，它不会自动增加唯一键计数器，则解决方法是为数据库添加负值。

重复的键值违反了唯一约束（EF Core和PostgresSQL）

1 个答案: